Tuesday, 5 May 2020

More climate change fun with the BBC

From the BBC:

More than three billion people will be living in places with "near un-liveable" temperatures by 2070, according to a new study.

Unless greenhouse gas emissions fall, large numbers of people will experience average temperatures hotter than 29C. This is considered outside the climate "niche" in which humans have thrived for the past 6,000 years...

Researchers used data from United Nations population projections and a 3C warming scenario based on the expected global rise in temperature. A UN report found that even with countries keeping to the Paris climate agreement, the world was on course for a 3C rise.

According to the study, human populations are concentrated into narrow climate bands with most people residing in places where the average temperature is about 11-15C. A smaller number of people live in areas with an average temperature of 20-25C.


Ho hum.

From National Geographic:

The tropics are regions of the Earth that lie roughly in the middle of the globe. The tropics between [sic] the latitude lines of the Tropic of Cancer and the Tropic of Capricorn. The tropics include the Equator and parts of North America, South America, Africa, Asia, and Australia.

The tropics account for 36 percent of the Earth's landmass and are home to about a third of the world's people.


So the hot areas between the tropics have much the same population density as north and south thereof. They are not concentrated into "narrow climate bands", they are at all latitudes (except the Arctic circles and deserts. And half of the world's population (3.5 billion people) live within this circle, which is almost entirely between the tropics (the emptiest bit of that circle is the half of PR China, which is north of the Tropic of Cancer).

The tropics are warm all year, averaging 25 to 28 degrees Celsius (77 to 82 degrees Fahrenheit). This is because the tropics get more exposure to the sun. Because of all that sun, the tropics don't experience the kind of seasons the rest of the Earth does.

So one source says "A smaller number of people live in areas with an average temperature of 20-25C" and the other says that one-third of the world's population lives in areas with average temperatures of 25 - 28C. Which source looks more reliable?

If you add an arbitrary increase, like 3C, you can predict that average temperatures will be about 29C. Easy. I'm sure there are already plenty of inhabited areas with average temperatures of 29C, if it's so terrible, why do people live there?

And so on.

13 comments:

DCBain said...

Yep, it's another of those damned "projections" - or "guesses" as normal people call them.

Bayard said...

"large numbers of people will experience average temperatures hotter than 29C."

"A smaller number of people live in areas with an average temperature of 20-25C."

Quite apart from the fact that the average of 20-25 is 22.5C and 22.5 + 3 = 25.5C, not 29C, is it a larger or a smaller number of people that will experience these temperatures?

The BBC, catering for the innumerate as well as the illiterate.

Mark Wadsworth said...

DCB, yes, it boils down to "if it gets warmer it will be warmer"

B, exactly. I find this infuriating.

Ted Treen said...

Weren't there 'studies' circa 1880 which projected that by 1920 most major cities' streets would be 15 feet deep in horse manure?

With most of these 'studies', manure seems to be a common factor.

ontheotherhand said...

I can't be bothered to research it, but right from the off the BBC is not good at being clear. It is not a 3 degrees rise as they report (every reader assuming from the temperature today), but a 3 degrees rise over pre-industrial levels. I'm sure if I went on I would find that this is not the central projection of the model, but the 90th percentile, and assumes that we do not adapt in any way etc. etc.

Mark Wadsworth said...

TT, exactly.

OTOH, yes, they exaggerate a bit, then take an unrepresentative example, then exaggerate that a bit, then round it up etc. I'm heartily sick of it.

JohnM said...

There's another issue.

If the world warms 3 degrees then that doesn't mean that everywhere gets 3 degrees warmer. The "consensus" is that the temperature at the poles will increase more than at the equator. Hence the fear of melting polar ice.

Mark Wadsworth said...

JM, excellent point. So to add to the list of mistakes, even if there were 3C warming (very unlikely), then it would be (say) 1C warmer at equator and 5C warmer at the poles, average 3C.

Sobers said...

There's also the fact that a 3 degree rise in average temps does not necessarily mean the maximum temps rise exactly in step. It can just mean that the daily minimums rise. Thats whats happened in the UK over the last 30 years, we don't have hotter summers, we just have milder winters and warmer nights all year round. Result average temps go up, maxima stay the same.

Mark Wadsworth said...

S, exactly. Which is probably a lot better for farmers and for everybody else. Hooray!

Frank said...

"...if it's so terrible, why do people live there?"

They're foreign, they don't know any better.
Or
They're foreign, they don't have the BBC to tell them what to do.

Which may be two ways of saying the same thing. ;-)

Blissex2 said...

«If you add an arbitrary increase, like 3C, you can predict that average temperatures will be about 29C. Easy. I'm sure there are already plenty of inhabited areas with average temperatures of 29C, if it's so terrible, why do people live there?»

I like this blog and the bloggers, but this is embarrassingly ridiculous. A change in average yearly temperatures of 3C in any area is a really big deal, and can impact sustainable population density a lot (by changing the local food supply). Also changes in 3C are averages over the whole globe, and some areas will have much bigger changes even as to yearly averages.

MY impression is the whole "climate change" thing is both undeniable and overblown, but this kind of criticism is really not helping.

Mark Wadsworth said...

F, I think it's because they know what they are doing.

B2, calm down. The 3C isn't going to happen. This is just the little boy crying wolf for the eight thousandth time.